Thermoplastic resins are plastics that are softened and plasticized by heating and are hardened by cooling. Thermoplastic resins are divided into: common plastics such as polyethylene, polypropylene, acrylic resin, styrenic resin, and vinyl resins; and engineering plastics such as polycarbonate, polyphenylene ether, polyamide, polyester, and polyimide resins.
Thermoplastic resins are widely used in numerous applications, including various household supplies, office automation equipment, and electric and electrical appliances owing to their superior processability and formability. There has been a continuous attempt to use a thermoplastic resin as a high value-added material by imparting specific properties as well as superior processability and formability to the thermoplastic resin, according to the kind and properties of products in which the thermoplastic resin is used. In particular, there have been various attempts to impart electrical conductivity to a thermoplastic resin and utilize the electrically conductive thermoplastic resin in the manufacture of automobiles, electric apparatuses, electronic assemblies, and electrical cables with electromagnetic wave shielding performance.
Electrically conductive thermoplastic resin is conventionally prepared from an electrically conductive thermoplastic resin composition obtained by mixing a thermoplastic resin with a conductive additive, such as carbon black, a carbon fiber, a metallic powder, a metal-coated inorganic powder, or a metallic fiber. To ensure a desired level of electrical conductivity of the electrically conductive thermoplastic resin, the conductive additive needs to be used in a significantly large amount. However, the use of the conductive additive in significantly large amounts can deteriorate impact resistance, which is one of the basic mechanical properties of the thermoplastic resin.
In addition, there have also been efforts to impart superior electrical conductivity to a thermoplastic resin using carbon nanotubes as a conductive additive.
However, when an electrically conductive thermoplastic resin is prepared by mixing a thermoplastic resin with carbon nanotubes and injecting the mixture using injection molding equipment, the carbon nanotubes show mobility and unexpected orientation due to shearing stress occurring during the injection. As a result, disconnection between the carbon nanotubes in the electrically conductive thermoplastic resin occurs, thus causing deterioration in electrical conductivity. Accordingly, where carbon nanotubes are used, the carbon nanotubes need to be added in a significantly large amount to the thermoplastic resin in order to ensure the desired electrical conductivity. The use of such large amounts of the carbon nanotubes, however, can deteriorate impact resistance, which is one of the basic mechanical properties of the electrically conductive thermoplastic resin.